Simplex Scientific, LLC (Simplex) is proposing to develop a medical device that can accurately measure hypovolemia due to hemorrhage from trauma which can lead to shock and ultimately death and which will be suitable for deployment at civilian and military trauma sites and during transport where motion-induced artifacts interfere with conventional technologies. There is an urgent need for a reliable, rapid, easy-to-use hypovolemia detector at the trauma site and during medical transport. After trauma, hemorrhage leads to blood loss and hemorrhagic shock, a leading cause for death among the young and healthy, especially in combat, because their bodies do not manifest overt symptoms until the later stages (Stage III+), which is associated with higher morbidity and mortality. Current methods cannot reliably detect early stages of hemorrhagic shock, as outward physical symptoms are unreliable, and first responders (FRs: usually EMTs or combat medics) often cannot estimate the blood volume lost even with external hemorrhage. Approximate indicators of hypovolemia (blood pressure and pulse pressure), require valid readings, which are difficult to obtain when the patient is in motion (ambulance or helicopter), and require knowing a patient's baseline numbers for accurate diagnosis. When a patient has stable vital signs (as they often do in Stage I or II hypovolemia), diagnosis can often only occur in a hospital. Thus, a reliable means to ascertain when a victim is in early-stage hypovolemia would allow FRs to provide oxygen to victims, and move them higher in triage than their overt symptoms might otherwise indicate, both of which would enhance outcomes and reduce mortality, all while reducing treatment costs. In this two Phase project, Simplex intends to create a portable device that can reliably and objectively identify when a trauma victim is in early-stage hypovolemia regardless of motion or baseline data. In order to demonstrate feasibility of this device in Phase I, we will attempt to validate our hypothesis, which is that there is a measurable reading that is consistent across all patients that can be used to identify when a patient is in early-stage hypovolemia. To do this, in Aim 1, we will study human subjects to obtain baseline measurements and measurements taken under stress using a lower body negative pressure chamber (a hypobaric chamber) to ascertain whether the measurement identified in preliminary studies is accurate across the target population (young and healthy persons). Then, in Aim 2, we will generate an algorithm to correlate our measurements to early-stage hypovolemia. In Aim 3, we will create a bread-board prototype device that should be able to identify early-stage hypovolemia regardless of baseline data. In Phase II, we will miniaturize this prototype device, ruggedize it for field us, and test it under field conditions. At the conclusion of this two-stage process, we should have a reliable and objective device capable of identifying early-stage hypovolemia in the field.